A power breaker of this type has been disclosed in, for example, DE 100 19 092 A1. The protective device, which, in a known manner, is in the form of an electronic overcurrent release, is in this case located in a front region of the power breaker behind a control panel. On the other hand, current transformers or current sensors, which detect measured values for the current in each of the poles of the power breaker and supply auxiliary power required for operating the protective device, are arranged on the rear side of the power breaker which is opposite the control panel. A cable harness connects these two regions of the power breaker. The electronic memory, which serves the purpose of storing characteristics and conversion factors which are dependent on the physical size and design of the power breaker, is arranged in the path of the cable harness.
A further known application of an electronic memory which is physically separated from the protective device is a rated current plug according to U.S. Pat. No. 4,958,252. In this case, the memory serves the purpose of recording operational events. In particular, the events include the number of switching operations and the level of the respectively interrupted current in order to determine from this the time for required maintenance work to be carried out on the power breaker.
Also known is an electrical switch having an electronic protective device and a memory which are connected via a parallel data bus (U.S. Ser. No. 4,996,646 A).
If an electronic memory of the abovementioned type is arranged in the power breaker such that it is physically separated from the protective device, a connection line or cable harness is required for there to be communication between these units. In this case, the electronic memory can be arranged in the path of the cable harness, as is described in the mentioned DE 100 19 092 A1. All of the interacting components and units are thus subjected to the disruptive influence of the magnetic, electrical and electromagnetic fields occurring in a power breaker. Since the sensitivity of electronic components and circuits to influences of this type is known, shields have been fitted in order to prevent disturbances to the operation of the protective devices (U.S. Ser. No. 5,303,113).
However, the increasing requirements placed on the switching capacity of power breakers lead to the electromagnetic influences on all of the electronic components of a power breaker also being increased correspondingly. Although there is extensive experience in controlling these influences, it appears to be desirable in the interest of safety to increase the electromagnetic compatibility (EMC) in particular of the electronic memory which is arranged separately.
In this case, at the forefront is the consideration that, in the case of communication between the protective device and the memory, address information as well as write and read information can be altered by an interference field which has accidentally been greatly increased. For example, it may be possible for a write operation to take place instead of a read operation without a user being capable of recognizing this. In certain circumstances, it is possible in this way to influence the behavior of the protective device, which can lead to undesired tripping of the power breaker or to this tripping being suppressed even though it is required.
It is obvious per se to eliminate these undesirable influences by using the internal write protection of the electronic memory. The memory modules (EEPROM) have for this purpose a separate input (WC=WRITE CONTROL) which cancels or establishes the write protection depending on the potential applied, as is described, for example, in U.S. Ser. No. 5,363,334. However, in a power breaker, the memory is not accessible, for example in the case of the arrangement in the path of a cable harness according to DE 100 19 092 A1.
It is therefore not possible to use a jumper which is conventionally provided. Even an electrical connection of the write protection input of a memory (EEPROM) is subject to difficulties, since an additional line required for this purpose is not available and undesirable additional complexity is required to install it retrospectively.